1. Field of the Invention
The present invention relates to a routing control method for a composite network whereby the most economical communication is achieved for a private network, for example, an international private network (IPNW), interconnecting a plurality of nodes by leased lines and operating in combination with public switched telephone networks (PSTNs).
2. Description of the Related Art
Generally, for economical communications, it is desirable that leased lines that can be hired at fixed rates be used as much as possible rather than public switched telephone networks for which rates are charged by metering. For international communications, however, the legal systems vary from country to country, and whether or not the use of leased lines is allowed depends on the communications regulations in each country. That is, some countries permit connections from leased lines to a public switched telephone network (hereinafter called public-private connections) for communication with a called party connected to that public telephone network, while in others (e.g., Malaysia), such connections are not allowed. Furthermore, even when public-private connections are allowed, some countries (e.g., Germany) allow such connections for facsimile communication only but prohibit connections for voice communication, whereas some countries (e.g., U.S.A.) allow such connections for both voice and facsimile communications. These and other reasons complicate the selection of economical routing.
It is therefore necessary to construct a composite network and design an effective numbering plan for connection between terminals in the network by considering such complicated circumstances as described above.
The numbering plan is usually different for access to a leased line than for access to a public network, which means different number dialing methods, requiring for the calling party to follow different and cumbersome operating procedures.
That is, the calling party has been required, each time, to judge by himself whether public-private connections are allowed, based on the destination country, the type of communication desired, etc., and to enter nonstandardized dial information to set up the optimum route that conforms to the applicable communications regulations.
However, in the prior art, a composite network routing control method has yet to be devised which automatically determines whether or not public-private connections are allowed, by examining the dial information entered from the calling party and judging the regulations on public-private connections applicable to the destination node, the type of communication desired, etc., and which selects the optimum route (the most economical route) under the applicable communications regulations.
Further, for leased lines, compression and multiplexing techniques are often employed to enhance network utilization, which in turn reduces the bandwidth per channel. In particular, when the bandwidth is as narrow as 16 kbps or 8 kbps, if dial information is sent out using the dual-tone multifrequency (DTMF) method that uses dual-frequency tones for transmission of a number, it may become difficult to accurately reconstruct the number at the receiving end. Therefore, in some cases, the number has had to be transmitted by using the pulse dialing method (10/20 PPS method) that depends on transmitting a required number of dial pulses within a prescribed time.
Since the 10/20 PPS method depends on generating a required number of pulses within a prescribed time for transmission of a number, as described above, the time required for transmission of the dial information inevitably increases with an increase in the number of digits contained in the dial information to be transmitted.
In such cases, therefore, and in particular, when the destination node is of the store-and-forward type, the number conversion is performed after all the digits constituting the dial information have been received, and after that, the converted dial information is sent out onto the PSTN. Thus, the time required to transmit dial information has resulted in an appreciable delay from the time the number is dialed by the calling party until the call is connected to the called party.
Accordingly, the prior art routing method for a composite network has had the following problems.
Firstly, the calling party is required, each time, to judge by himself whether public-private connections are allowed, based on the destination country, the type of communication desired, etc., and to enter nonstandardized dial information for connection to the destination via a leased line or a PSTN.
Secondly, in transmitting dial information, and in particular, when the destination node is of the store-and-forward type, the number conversion has to wait until after all the digits constituting the dial information have been received, and after that, the converted dial information is sent out onto the PSTN; thus, the time required to transmit the dial information causes an appreciable delay from the time the number is dialed by the calling party until the call is connected to the called party.